#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
int main()
{
	int nums[] = { 0 ,1,2,3,4,6,7};
	int n = sizeof(nums)/sizeof(nums[0])+1;
	int sum = n * (n - 1) / 2;
	int sums = 0;
	int i = 0;
	for (i = 0; i < n - 1; i++)
	{
		sums += nums[i];
	}
	printf("%d", sum - sums);
	return 0;
}